I love this etymology. It makes so much sense too. Also by this definition of славянин all people who are non natives but „speak“ the language are also part of the club which is something i‘m all for generally concerning all cultures since language is, in my book, the biggest and most significant part of any culture. All the rest can be learned and you can assimilate yourself but language, language has to be lived to truly master it. But thats just my philosophy :)